When drilling or completing wells in earth formations, various fluids typically are used in the well for a variety of reasons. The fluid may be either water-based or oil-based. For the purposes herein, such fluid will be referred to as “well fluid.” Common uses for well fluids include: lubrication and cooling of drill bit cutting surfaces while drilling generally or drilling-in (i.e., drilling in a targeted petroliferous formation), transportation of “cuttings” (pieces of formation dislodged by the cutting action of the teeth on a drill bit) to the surface, controlling formation fluid pressure to prevent blowouts, maintaining well stability, suspending solids in the well, minimizing fluid loss into and stabilizing the formation through which the well is being drilled, minimizing fluid loss into the formation after the well has been drilled and during completion operations such as, for example, perforating the well, replacing a tool, attaching a screen to the end of the production tubulars, gravel-packing the well, or fracturing the formation in the vicinity of the well, displacing the fluid within the well with another fluid, cleaning the well, testing the well, fluid used for implacing a packer, abandoning the well or preparing the well for abandonment, and otherwise treating the well or the formation.
A variety of compounds may be added to well fluids to enhance performance. Among these compounds are fluid loss control agents, which act by coating the walls of the wellbore as the well is drilled, with a thin layer of low-permeability filter cake. The filter cake helps to reduce the amount of base fluid lost to the formation and prevents undesirable variations in the density and rheology of the drilling fluid. Additionally, the filter cake helps prevent formation damage in the reservoir, which may be caused by blockage of formation pores through invasion of wellbore fluid. Filter cake also provides a barrier to prevent the influx and efflux of drilling fluids between the wellbore and the formation. Suitable fluid loss control additives, for both water-based and oil-based drilling fluids include modified starches, synthetic resins, modified lignites, asphaltic compounds, gilsonites, and a wide range of other polymeric and non-toxic fluid loss control materials. Such fluid loss control agents may be generally used in drilling fluids, or may be used in gel pills used to prevent fluid loss in a particular zone of the wellbore.
The role of the fluid loss characteristics of the well fluid demands that the properties of the well fluid are carefully monitored throughout the operation, and that corrective measures are taken in time to maintain required specifications of the fluids in the operation. Standard equipment for evaluating fluid efficiency, e.g. filter cake breaker fluid efficiency, includes a high temperature/high pressure (“HTHP”) fluid loss cell. In such HTHP cells, after the filter cake is established, the HTHP cell is opened to exchanged or replace the fluids in the HTHP cell, thereby releasing the temperature and pressure, from the cell. Tests are subsequently run on the replacement fluid.
Despite many valuable contributions from the art, it would be beneficial to develop improved equipment and methods for testing well fluids.